1. Field of the Invention
The present invention relates to a method and apparatus for filling aerosol cans of the so-called "pressure-barrier" type. These cans are formed from a rigid receptacle having an interior with two compartments separated by a mobile or deformable partition, one of the compartments being designed to contain a liquid or pasty substance to be packaged and the other a pressurized propellent gas or liquid which is thus prevented from coming into contact with the substance to be packaged.
2. Description of the Prior Art
Conventionally, the mobile or deformable partition consists of a pocket which is made either of a flexible plastic material, such as low-density polyethylene, or of high-grade coated aluminum. This pocket has a single opening. The diameter of this opening may be substantially the same as that of the opening of the receptacle and, in this case, the pocket is designed so as to be held in the crimping which fixes the sealing valve is onto the receptacle, or the diameter of the opening is approximately the same as that of the receptacle and, in this case, the pocket is designed so as to be held in the crimping of a flange which forms the lid and onto which the valve is crimped.
Conventionally, filling is performed as follows:
the pocket is placed inside the receptacle and filled with the substance to be packaged, PA1 the receptacle is sealed by crimping either the valve or the flange carrying the valve, PA1 a propellent medium is introduced into the other compartment in the can by means of a hole which is provided in the bottom of the can and sealed by an impermeable rubber stopper through which a hollow needle is passed in order to perform filling.
In another system, the mobile or deformable partition consists of a piston which moves inside the can, sealing means being provided between this piston and the internal walls of the can. The filling method is the same as that described above. Hereinafter, the term "deformable partition" will also embrace a mobile partition of this type.
Another system has recently been proposed (Aerosol Report, Svitila et al, volume 23, No. 6/84, pages 286-299) from lecture given September, 1983, in which the propellent medium is formed in a sealed pocket which contains metered amounts of two solid or liquid chemical products which, when brought into contact with each other, release a certain amount of gas. Initially, the desired amount of substance to be packaged is introduced into the receptacle, then the pocket containing the gas-generating products and a small quantity of gas already present is introduced into it and, finally, crimping of the valve or of the flange carrying the valve is performed. During use, the pocket expands owing to the action of the small quantity of gas which it contains, and this expansion leads to gradual opening of the partitions separating the gas-generating products with the result that most of the propellent gas is formed during use.
These methods have the drawback that the substance to be packaged is filled either in the open air or inside a controlled-atmosphere enclosure which is necessarily large and, hence, costly if contamination by oxygen or by microbial germs is to be eliminated.
On the other hand, even if this operation is performed in a sterile atmosphere, the substance to be packaged can be modified, when it comes into contact with this atmosphere, by dissolution of the gas of the protective atmosphere, or by removal out of the volatile matter which is dispersed through the large area of the controlled-atmosphere enclosure.